We have found that thyroid epithelial cells in inverted follicles transport H20 at rates of about one-sixth the rate of kidney cells. We have found that when the apical surface of thyroid epithelial cells begin to adhere to the surface of a collagen gel, it is by a specialized region of the surface, the site of a pseudopod and not of microvilli. We have identified cells migrating as single cells from follicles embedded in or on a collagen gel to be fibroblasts that are trace contaminants of the original culture.